add crispr_vector_seq method to generate crispr vector sequences
the crispr_vector sequence is split int two and the two halves are swapped around and rejoined, this places the crispr in the middle of the sequence
v0.011

    Add method to generate crispr_vector sequences.
merge synthetic cassette features if we get duplicates after recombination
v0.012

	Fixed bug where dual synthetic cassette features created.
Merge branch 'master' into andrew_exon_ranks